There are two major types of cells grown in vitro: suspension cells (anchorage-independent cells) and adherent cells (anchorage-dependent cells). Suspension or anchorage-independent cells can multiply, in vitro, without being attached to a surface. In contrast, adherent cells generally attach to a surface in vitro during culture and proliferation, referred to herein generally as cell processing. Additionally, some typically non-adherent cells can proliferate on a surface that promotes adherent cell growth.
Cells are commonly cultured in a growth medium within containers (e.g., polystyrene) placed in enclosed incubators. In addition to providing a certain degree of isolation from pathogens, the incubators generally maintain a constant temperature, and a constant gas mixture.
Adherent cell culture systems require a surface on which to culture cells, such as a culture container or microcarrier (such as gelatin, porous glass, collagen or cellulose). The surface may also be coated with an extracellular matrix to increase adhesion properties. Feeder cells may also be used to coat the surface to provide a more adherent surface as well as providing nutrients to cultured cells. When the cells are ready to harvest, they must be removed from the culture surface. Adhesion of the cultured tissue to the surface generally makes removal a challenging task. An enzyme can be used to separate the cultured cells from the culture surface. Use of such enzymes or other chemicals or methods to separate cultured cells from the surface can cause damage to the tissue and even to the cultured cells, themselves.